Electron tubes, in a retarding field circuit arrangement



arch 17, 1936. R. URTEL 2,034,011

ELECTRON TUBES IN A RETARDING FIELD CIRCUIT ARRANGEMENT Filed Jan. 6, 1955 INVENTOR RU D OLF URTE].

ATI'ORN EY Patented Mar. 17, 1936 UNETED STATES PAT FFEQE ELECTRON TUBES, IN A RETARDING FIELD CIRCUIT ARRANGEMENT Germany Application January 6, 1933, Serial No. 650,495 In Germany March 24, 1932 5 Claims.

With a thermionic tube connected in a retarding field circuit arrangement, if full utilization of the properties of such circuit is to be obtained, it is necessary that the cathode of the tube show a definite saturation point for emission current. In actual tubes the saturation point is, however, more or less indefinite and is not reached when normal voltages are applied to the tube elements. Application Serial No. 654,091 filed Jan. 28, 1933 discloses ways and means of overcoming the disadvantages of this actual lack of definiteness of saturation and the present invention discloses other circuit arrangements for attaining the same end.

According to the invention instead of an auxiliary-grid arrangement as suggested in the patent application Serial No. 654,091, being provided inside the tube to be used in the circuit scheme, a resistance R is included in the joint circuit grid and plate circuits which, regardless of the applied potential, supplies a constant current as illustrated in Fig. 1. In this figure the battery I6 has its positive terminal connected to the control grid and its negative terminal to the cathode through a resistor R, the grid current Ig may then be read on an ammeter connected as shown. A second battery E1; has its positive terminal connected to the plate or anode and its negative terminal to the end of resistor R as shown, the plate current Ia may then be read on a second ammeter connected as shown. The fall of voltage across the said resistance conditions the presence of a compensating voltage,

in order that the retarding electrode may again be at a potential difiering but slightly from the filament. In this formula Ia is the value of the plate current, Ig the value of the grid current, R. the value of the resistor common to the grid and plate circuits and Ea is the voltage between anode and cathode in the absence of R. If the cathode current through R. were to increase, the grid becomes less positive with respect to the cathode, thereby decreasing the grid current directly as fewer electrons are attracted to it and the plate current is also decreased by the mutual conductance of the grid to plate of the tube. By selecting R of the proper value the total current between the cathode and the cold elements of the tube may thus be maintained substantially constant, irrespective of voltage variations. The resistance would be represented, for instance, by a screen-grid tube. Hence, according to this invention, and as illustrated in Fig. 2

(seeing that solely the resistance characteristics I of this tube are to be utilized), a screen-grid tube I provided, for instance, in the radio frequency amplifier stage of a receiver arrangement is employed to act as a resistance R in the joint circuit Ig+Ia of the tube 2 used in the retardingfield scheme. Also by this means conditions are obtained so that cathodes presenting a definite saturation in the retarding-field tube will be dispensable. As shown in Fig. 2 the tunable input circuit of screen grid tube I comprises a coil 3 shunted by a variable condenser 4, the screen 5 being given a positive potential by a battery l6 and the plate l2 of tube 2 a positive potential by a battery H. In the plate circuit of amplifier l is a parallel resonant circuit com prising coil l0 and variable condenser H, the high potential end of coil H] being connected to plate 6 through a condenser 9. A conductance path including coil 8 and lead !4 connects the cathode of tube 2 with the plate 6, the direct plate current 18, of tube 2 passing over this path to the plate 6 as does also the grid current Ig of tube 2. The grid current of tube 2 is supplied by a battery l8 through a resistor l5. From the described arrangement it is apparent that the platecathode resistance of the screen grid tube I takes the place of resistor R of Fig. 1 and that the total current through tube 2 and battery I! up to the point l9 remains substantially constant irrespective of variations in the radio frequency current through the plate of tube I. In other words the high impedance of screen grid tube I may replace resistor R of Fig. 1 without interfering with the function of tube l as a radio frequency amplifier. At point IS the total current Ia+I divides, the portion Ig flowing through resistor IE to the grid of tube 2 while the portion Ia passes to the plate I 2 through coil l0. Any desired means (not shown) may be used for impressing the radio frequency currents to be amplified on the control grid circuit 3, 4 of tube l and any desired means (not shown) used for transferring the amplified currents from its plate circuit including coil I0. Condensers l and I3 are the usual by-pass condensers. Due to the high plate impedance of the screen grid tube for alternating current, the arrangement provides a large control of the voltage of the grid of tube 2 and at the same time the battery I! need not be as large as would be necessary if an equal resistance value in the form of a single resistor such as R of Fig. 1 Were used.

What is claimed is:

1. An arrangement for the production of a substantially constant current, comprising the combination of a vacuum tube having a control grid, cathode and anode, an output circuit connecting said cathode and anode and including a source of potential connected to maintain said anode constantly at a positive potential with reference to said cathode, an input circuit connecting said cathode and control grid, a source of potential for maintaining said grid at a positive potential with reference to said cathode and an element having a high resistance connected in both said input and output circuits the resistance of said element being designed to maintain the total current therethrough substantially constant irrespective of whether the cathode current of said tube is saturated.

2. In a device of the class described, the combination of a vacuum tube having a control grid, cathode and anode, an output circuit connecting said cathode and anode and including a source of potential connected to -maintain said anode constantly at a positive potential with reference to said cathode, a grid circuit connecting said cathode and control grid and including a source of potential connected to maintain said grid at a positive potential with reference to said cathode,

and a second vacuum tube having its plate conbination of a vacuum tube having a control grid, cathode and anode, an output circuit connecting said cathode and anode and including a coil and variable condenser connected in parallel, a grid circuit connecting said cathode and control grid and a second vacuum tube having its plate conductively connected to the cathode of said first named tube and a circuit connecting its cathode to the anode of said tube, said circuit including the series connection of a source of positive potential and said coil, said second tube having a control grid and a screen grid, means for applying a positive potential to said screen grid, atunable input circuit connecting said control grid and cathode, the grid circuit of said first named tube comprising a source of potential having its negative terminal conductively connected to said screen grid and also being arranged to provide a conductive connection to the cathode of said screen grid tube.

'5. In adevice of the class described, the combination'of a vacuum tube having a control grid, cathode and anode, a coil, a conductive connection between one end of said coil and said anode,

,a'source of potential having its negative terminal conductively connected to the other end of said coil and its positive terminal to said grid, a second vacuum tube having a cathode, a control grid and a plate, a conductive connection between said-plate and the cathode of said first tube, means coupling said plate to the first named end of said coil, an input circuit connecting the grid and cathode of said'second tube and a source of potential having its negative terminal connected to the cathode of said second named tube and its positive terminal to the negative terminalof said firstnamed potential source.

RUDOLF URTEL. 

